Method of plasma etching

Abstract

A method of plasma etching a silicon carbide workpiece includes forming a mask on a surface of the silicon carbide workpiece, performing an initial plasma etch on the masked surface using a first set of process conditions, wherein the plasma is produced using an etchant gas mixture which includes i) oxygen and ii) at least one fluorine rich gas which is present in the etchant gas mixture at a volume ratio of less than 50%, and subsequently performing a bulk plasma etch process using a second set of process conditions which differ from the first set of process conditions.

What is claimed is: 
     
       1. A method of plasma etching a silicon carbide wafer, including the steps of:
 forming a mask on a surface of the silicon carbide wafer; 
 performing an initial plasma etch comprising etching the masked surface using plasma under a first set of process conditions, wherein the plasma is produced using an etchant gas mixture which includes i) oxygen and ii) at least one fluorine rich gas which is present in the etchant gas mixture at a volume ratio of less than 50%; and 
 subsequently performing a bulk plasma etch process comprising etching the silicon carbide wafer using plasma under a second set of process conditions which differ from the first set of process conditions. 
 
     
     
       2. A method according to  claim 1  in which the fluorine rich gas is present in the etchant gas mixture at a volume ratio in the range 0.1-20%. 
     
     
       3. A method according to  claim 1  in which the at least one fluorine rich gas is CF 4  and/or SF 6 . 
     
     
       4. A method according to  claim 1  in which the plasma etching of the silicon carbide wafer is performed to provide one or more vias. 
     
     
       5. An apparatus for etching a silicon carbide workpiece including: a chamber; a workpiece support positioned in the chamber; a gas supply and pumping arrangement for providing etchant gases to the chamber; and a control arrangement configured to control the apparatus, including the gas supply and pumping arrangement, to perform a method according to  claim 1 . 
     
     
       6. A method according to  claim 1  in which the fluorine rich gas is present in the etchant gas mixture at a volume ratio in the range 0.1-10%. 
     
     
       7. A method according to  claim 1  in which the fluorine rich gas is present in the etchant gas mixture at a volume ratio in the range of 0.5-7%. 
     
     
       8. A method according to  claim 1  in which the fluorine rich gas is present in the etchant gas mixture at a volume ratio of about 1.5%. 
     
     
       9. A method according to  claim 1  in which the mask is a metallic mask. 
     
     
       10. A method according to  claim 9  in which the mask is a nickel mask. 
     
     
       11. A method according to  claim 1  in which the surface of the silicon carbide wafer on which the mask is formed is unpolished. 
     
     
       12. A method according to  claim 11  in which the surface of the silicon carbide wafer on which the mask is formed is lapped. 
     
     
       13. A method according to  claim 1  in which the initial plasma etch is performed to an etch depth of at least 250 nm. 
     
     
       14. A method according to  claim 13  in which the initial plasma etch is performed to an etch depth of at least 700 nm. 
     
     
       15. A method according to  claim 1  in which the etchant gas mixture further includes an inert carrier gas. 
     
     
       16. A method according to  claim 15  in which the inert carrier gas is a noble gas. 
     
     
       17. A method according to  claim 15  in which the inert carrier gas is argon.